<template>
    <ul class="list">
        <li class="item" v-for="item of letters"
            :key="item"
            :ref="item"
            @touchstart="handleTouchStart"
            @touchmove="handleTouchMove"
            @touchend="handleTouchEnd"
            @click="handleLetterClick"
        >{{item}}</li>
    </ul>
</template>
<script>
    export default{
        name:'CityAlphabet',
        props:{
            cities:Object
        },
        computed:{
          letters (){
                const letters=[]
                for(let i in this.cities ){
                    letters.push(i)
                }
                return letters
            }
        },
        data(){
            return{
                touchStatus:false
            }
        },
        methods:{
            handleLetterClick(e){
                this.$emit('change',e.target.innerText)
                console.log(e.target.innerText)
            },
            handleTouchStart (){
              this.touchStatus=true
            },
            handleTouchMove (e){
               if(this.touchStatus){
                   const startY=this.$refs['A'][0].offsetTop
                   const touchY=e.touches[0].clientY-79
                   const index=Math.floor((touchY-startY)/20)
                   if(index>=0&&index<this.letters.length){
                       this.$emit('change',this.letters[index])
                   }
               }
            },
            handleTouchEnd (){
               this.touchStatus=false
            }

        }
    }
</script>
<style lang="stylus" scoped>
    .list
        display:flex
        flex-direction :column
        justify-content:center
        position:absolute
        top:1.58rem
        right:0
        bottom:0
        width:.4rem
    .item
        line-height:.4rem
        text-align:center
        color:$bgColor

</style>